Investment Securities Available for Sale with Gross Unrealized Losses Aggregated by Investment Category and Length of Time Individual Investment Securities Have Been in Continuous Position (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012 Investment
Investments, Unrealized Loss Position [Line Items]
Number of investment positions in continuous loss position less than twelve months	19
Number of investment positions in continuous loss position more than twelve months	4
Number of investment positions in continuous loss position	23
Fair value of securities in continuous loss position more than twelve months	$ 16,560
Fair value of securities in continuous loss position more than twelve months	1,681
Fair value of securities in continuous loss position	18,241
Gross unrealized losses of securities in continuous loss position less than twelve months	116
Gross unrealized losses of securities in continuous loss position more than twelve months	50
Gross unrealized losses of securities in continuous loss position	166
Agency Collateralized Mortgage Obligations
Investments, Unrealized Loss Position [Line Items]
Number of investment positions in continuous loss position less than twelve months	3
Fair value of securities in continuous loss position more than twelve months	3,049
Gross unrealized losses of securities in continuous loss position less than twelve months	1
Agency CMO
Investments, Unrealized Loss Position [Line Items]
Number of investment positions in continuous loss position less than twelve months	10
Number of investment positions in continuous loss position more than twelve months	2
Fair value of securities in continuous loss position more than twelve months	9,798
Fair value of securities in continuous loss position more than twelve months	1,105
Gross unrealized losses of securities in continuous loss position less than twelve months	86
Gross unrealized losses of securities in continuous loss position more than twelve months	4
Agency mortgage-backed securities
Investments, Unrealized Loss Position [Line Items]
Number of investment positions in continuous loss position less than twelve months	1
Fair value of securities in continuous loss position more than twelve months	2,075
Gross unrealized losses of securities in continuous loss position less than twelve months	9
Municipal Notes
Investments, Unrealized Loss Position [Line Items]
Number of investment positions in continuous loss position less than twelve months	5
Fair value of securities in continuous loss position more than twelve months	1,638
Gross unrealized losses of securities in continuous loss position less than twelve months	20
Collateralized Mortgage Obligations Issued By Private Enterprise
Investments, Unrealized Loss Position [Line Items]
Number of investment positions in continuous loss position more than twelve months	1
Fair value of securities in continuous loss position more than twelve months	202
Gross unrealized losses of securities in continuous loss position more than twelve months	28
Mutual Funds
Investments, Unrealized Loss Position [Line Items]
Number of investment positions in continuous loss position more than twelve months	1
Fair value of securities in continuous loss position more than twelve months	374
Gross unrealized losses of securities in continuous loss position more than twelve months	$ 18